As I understand it, the 3G service for T-Mobile operates on a different frequency than AT&T 3G so I'm not sure if the 3G for T-Mobile will work?
BTW I found this guide on Unlocking iPhone 3G with Yellowsn0w pretty useful!
I finally upgraded to 2.2 and quickpwnd it. However I had to drive around the block from my apt. to pick up a wifi single coming from a used car dealership in order from me to install yellowsn0w. LOL!
Luckily after I installed, it picked up my Tmobile signal within seconds...I was freezing my butt off!
I'm having a problem here. I upgraded and jailbroke 2.2 used the newest yellowsn0w but I keep losing my signal. I am on T-Mobile and the the phone keeps searching for signal. And when it does have signal it shows full bars but I cannot make calls. Any ideas?